1. Field of Invention
This invention relates to rotational molding, in particular, to a method and molding composition to reinforce surfaces of parts formed by rotational molding.
2. Brief Statement of the Prior Art
Hollow-form plastic parts such as outdoor signs, tanks and containers are commonly formed by rotational molding. In rotational molding, polymer particles are charged to a rotational mold which is closed and heated to the melt temperature of the polymer particles while rotating the mold about its major and minor axes for a time sufficient to form the molded part. The mold is then cooled to a demolding temperature, opened and the molded product is ejected. A limitation of this molding process is that the walls of rotationally molded parts are substantially uniform in thickness, precluding formation of parts with integrally formed regions of greater wall thickness such as ribs, bosses and fillets. Also, the rotational molds are subjected to repeated thermal cycling and heavy usage which frequently distorts the sealing flanges of the mold, causing the mold to fail to seal tightly, resulting in loss of resin through cracks in the parting line of the mold.